1. Field of the Invention
The present invention relates to PCM telephony systems and more Particularly to an interface system for enabling different complements of port circuits, selected by the user, to be interfaced with the PCM telephony system for providing greater flexibility in the design of PCM telephony systems to satisfy different user applications.
2. Description of the Related Art
The present invention is especially suitable for providing a flexible interface system for interfacing different complements of port circuits to a PCM telephony switching system such as described in U.S. Pat. No. 4,228,536 issued Oct. 14, 1980 to K. Gueldenpfennig and C. J. Breidenstein and assigned to Redcom Laboratories, Inc. This is a distributed PCM time division digital switching system. The interface system of the invention is also especially suitable for use in telephone switching systems in port boards and port circuits of PCM time division multiplex switching systems such as described in U.S. Pat. No. 4,805,172 issued Feb. 14, 1989 to C. A. Barbe and B. G. Littlefield and assigned to Redcom Laboratories, Inc. for enabling the user of the system to configure the port circuits or port boards of the switching system to provide different applications including connections of data representative of voice signals to N lines or trunks where N is limited only by the number of time slots available to the port circuit and to provide connections for data representing digital communication data signals, such as used in conferencing.
In PCM telephony, data representing different signals is multiplexed in sequential time slots along PCM highways. These highways are connected to port circuits which contain coding and decoding devices for changing analog (e.g., voice) signals into pulse codes and vice versa, digital communication signal handling devices, and even video signal handling devices, all of which require different complements and/or numbers of sequential time slots. Accordingly, port circuits have been designed specifically for different applications and telephony switching systems which have heretofore been provided, such as shown and described in the above-referenced patents, have port circuits or port boards which are dedicated to specific applications (i.e., different combinations of line or trunk circuits and/or digital communication signal handling circuits). Users of telephony systems oftentimes require differently configured port circuits to meet their applications. Some users may wish to design their own port circuits. It is desirable to provide the flexibility for differently configured port circuits and to enable users to design their own circuits. However, the telephony switching system architecture, if opened to various port circuit designs and configurations, renders the system vulnerable to damage by the user configured port circuits and may violate security by exposing calls which may contain private information and/or programming codes of a secret nature.